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DURHAM, N.H. -- The upcoming Leonid meteor shower
may be an entertaining light show for sky-watchers, but
it will be a definite hazard to orbiting sensors, including a
University of New Hampshire instrument.

Eberhard Moebius of the UNH Institute for the Study
of Earth, Oceans and Space, says even tiny dust
particles, not considered dangerous to most satellites,
could irreparably damage the UNH-developed Solar
Energetic Particle Ionic Charge Analyzer (SEPICA) now
orbiting between the Earth and Sun aboard NASA's
Advanced Composition Explorer, or ACE.

That's why he and other scientists are planning to tilt
ACE to move the detectors out of harm's way, or so they
hope. Its axis now pointing toward the sun, ACE will be
turned 20 degrees by technicians at NASA's Goddard
Space Flight Center one day before the Nov. 17 Leonid
meteor shower.

(The Leonid storm this year peaks at 2:43 p.m. on Nov. 17,
so the United States will miss the highlight, although
remnants might make interesting viewing after midnight).

SEPICA examines the composition of accelerated
particles from solar flares and is designed to measure the
temperature at their origin. It uses a detector similar to
a Geiger counter, in which gas is trapped within very thin
window-like apertures. For these thin windows, even the
smallest dust grains trailing Comet 55P/Tempel/Tuttle
are like bullets.

"As one of my colleagues said, for the ACE satellite, it
takes the one rock with our name on it," says Moebius
with a wan smile. But it's not large chunks of meteoroid
that have Moebius and colleagues concerned. The smaller,
more numerous particles, even dust, pose a greater
hazard, since "the smaller in size you go, the more you
have," Moebius points out.

In addition, ACE will be closer than any other spacecraft
to the Leonid meteor stream, a dubious honor, Moebius
points out.

The Leonid meteor shower is seen every November, but it
rises to storm conditions every 33 years. It is caused by
the countless fragments and particles trailing the Comet
55P/Tempel/Tuttle as it comes close to the Earth this
year.

Yes, they put on a spectacular light show, even Moebius
admits. Back in 1966, some sky-watchers counted more
than 100,000 meteors an hour.

SEPICA "could take a few thousand hits if we don't do
anything," Moebius explains. A project team met in
mid-October and decided to tilt the axis. "And, with that,
we'll ride out the storm."

Plans also call for technicians to shut down SEPICA's
high voltage because a stray impact could cause electric
charges. "So, there may be a major solar flare happening
at that time, and we'll miss it," says Moebius, who saw
some of his work destroyed in the 1996 explosion of the
CLUSTER mission. "But I think we are willing to pay that
price."

He adds that SEPICA has already uncovered significant
information concerning the source of solar flare particles
and Moebius hopes to continue to receive data, especially
since solar flare activity is expected to increase in
upcoming months.